Utah Lake Carp Recruitment Control Project

Early settlers introduced several thousand European carp, Cyprinus carpio into Utah Lake between 1882 and 1903 where they quickly established and rapidly dominated Utah Lake’s fisheries (Heckmann et al. 1981). Along with the many ecosystem abuses that the settlers inflicted on Utah Lake, invasive carp via bioturbation caused the near complete loss of macrophytes (aquatic plants) as well other highly detrimental direct and indirect impacts (Richards and Miller 2019). These resulted in a rapid transition from a healthy clear water state to a degraded turbid state (Richards and Miller 2019, Scheffer et al. 1993, Vilizzi, Tarkan, and Copp 2015). A carp removal program was initiated in 2009 to reduce carp impacts when their biomass was estimated to be well over 50,000 tons and 95% of total fish biomass in the lake (Walsworth et al. 2020) (Figure 1). Despite program efforts, carp continue to thwart restoration efforts including the transition reversal from a highly resistant turbid state to a clearer stable state and a more balanced fishery (Richards and Miller 2019, Scheffer et al. 1993, Walsworth et al. 2020, Walsworth and Landom 2021). 

Utah Lake’s carp removal program is somewhat of a mixed success story. By 2017 and 2018, the program had reduced carp biomass to roughly 25% of the 2009 levels (Figure 1) and over 10,000 tons of carp have been removed from the lake since its inception (Walsworth et al. 2022). 

Unfortunately, preliminary analyses show that carp biomass has remained stable or has increased since 2017/2018, almost to pre 2012 levels (Figure 1) and there is no evidence that the number of carp per acre or carp biomass catch per unit effort (CPUE) in 2021 was different than years 2013 to 2018 (Walsworth et al. 2022). Also, removal methods continue to rely on netting of adult fish (Walsworth et al. 2022). It is apparent that lake conditions (e.g., high water events, shallow water, etc.) and carp behavior prevent further reduction by netting large sized fish alone. Other control methods are being considered including bait poisoning and introduction of infertile males (Walsworth et al 2022), neither of which in our opinion holds promise

The most effective method to reduce and maintain the carp population below ecosystem level impacts in Utah Lake is to target their most vulnerable stage, the egg (and larval) stage, known as the recruitment stage. 

Carp broadcast spawn adhesive eggs preferably on to aquatic vegetation or hard substrates in shallow water areas with low oxygen (hypoxic) levels. This reproductive strategy evolved to help reduce predation of vulnerable egg and larval stages from small fish predators and eliminated the need for parental care (Poole and Przemyslaw 2019, Przemyslaw et al. 2012, Walsworth et al. 2020). We have witnessed spawning activity of hundreds of carp in spring months in Utah Lake on dozens of occasions. These fish are near-oblivious (e.g., ‘they lose their minds’) to our presence, even in ankle deep water often where the substrate appears to be unsuitable (e.g., mud and silt) and recruitment survival rates low.

This pilot project encompasses a limited area of the lake; hence the carp recruitment control project will need to be expanded in area and continued for many years. In addition, we postulate that once carp levels are reduced to a threshold level via egg removal, restoration, and establishment of aquatic macrophytes will lead to less turbid conditions and small visual predators including Utah chub, bluegill, yellow perch, white bass, notonectids, predacious diving beetles, etc. will be able to maintain threshold level carp populations by feeding on their eggs and larvae.  

Our ultimate goal for Utah Lake is a well-balanced fishery with a more naturally functioning ecosystem including establishment of extensive macrophyte beds that maintain a clearer-water stable state.

Project Site

We will reduce carp recruitment using egg/larval removal mats placed along the northeast shoreline of Utah Lake between Lindon Marina and TSSD outfall (Figure 2), herein referred to as Mickelson Bay. Shoreline area covered with egg mats will be approximately 6000 ft2.

Figure 2. Location of carp recruitment control project. Spawning/egg removal mats will be placed along shoreline between Lindon Marina and TSSD outfall. 

Materials

Mats will be made of non-woven geotextile pond underlayment material locally sourced and similar to: https://www.aquascapeinc.com/products/geotextile-underlayment-roll or from specially designed fish egg mats not yet sourced. We will initially use four rolls of 5ft x 300ft material = 5ft x 1200 ft = 6000 ft2 spawning area. Rolls will be cut into 20 ft mat sections to aid in retrieval and egg removal. Each mat will be secured along lake shore in several inches of water adjacent to other mats to form a continuous egg laying area. Mats will be secured in each corner using 2 ft rebar. Different materials and setup will be dependent on funding and timing.

Control Dates

Carp typically spawn at water temperatures between 18 and 24 C. This temperature range can last up to a month on Utah Lake, usually in May. We will closely monitor the start of spawning when temperatures in shallow areas of the control project area approach 180 C and beginning with first arrivals. We will then remove eggs daily until the last spawning activity is observed.

Egg Removal and Research Methods

Our team will, 1) place and secure mats in the afternoon, 2) retrieve mats the next day in mid-morning after early morning spawning activities, 3) dry mats in sun along shoreline for 2 to 3 hours depending on temperature, sunlight, and inspection of eggs to insure they are desiccated and 4) replace and secure mats in midafternoon. This protocol will be repeated for the duration of spawning season at the Lindon Bay site (Figure 2). We will estimate the number of eggs removed either by actual count subsample estimates or from developing an egg/biomass ratio. We will also develop best methods for removal of eggs from mats to make counts. We will monitor spawning temperature, duration, and other notes.

A female carp can lay between 300,000 and 1,000,00 eggs over a breeding season with egg to larval survivability typically near 80% (citations).  We estimate that at a minimum 100 adult females will lay eggs on the mats. This equates to the potential removal of approximately 24 million to 80 million viable carp eggs and larvae (fry) from the system. 

We will document all our methods and publish findings in collaboration with volunteers.

Continued and Expanded Recruitment Control

We will expand mat deployment to cover as much shoreline spawning habitat as possible in coming years using volunteers, technicians, and agencies who are encouraged by our success. We expect to deploy hundreds of egg mats at least along the shorelines of Goshen Bay, areas in Provo Bay, Lindon Bay, and other areas where State fisheries biologists recommend are likely carp spawning areas.

After demonstrating our success at reducing carp recruitment, we will recommend that the adult carp removal program using nets continue at its current level but increase monitoring of other fish species catch. There are almost no data on fish species distributions, size classes, diets, biomass, and abundances other than carp and June Suckers. This information is critical for developing fisheries food web models, and for scientifically managing and restoring the lake ecosystem.

Personnel will consist of Dr. Richards and Dr. Miller, part time use of WFWQC interns when available, student volunteers as part of science project, and other non-paid volunteers. We will also solicit additional funding from other sources after demonstrating our success. 

Heckmann, Richard A.; Thompson, Charles W.; and White, David A. (1981) “Fishes of Utah Lake,” Great Basin Naturalist Memoirs: Vol. 5 , Article 8. Available at: https://scholarsarchive.byu.edu/gbnm/vol5/iss1/8

Landom, K.L. 2010. Introduced Sport Fish and Fish Conservation in a Novel Food Web: Evidence of Predatory Impact. M.S. Thesis. Utah State University, Logan, UT.

Poole JR, Bajer PG (2019) A small native predator reduces reproductive success of a large invasive fish as revealed by whole-lake experiments. PLoS ONE 14(4): e0214009. https:// doi.org/10.1371/journal.pone.0214009

Richards, D.C. and T. Miller. 2019. Factors Effecting the Ecological Health and Integrity of Utah Lake with a Focus on the Relationships between Water Column Regulators, Benthic Ecosystem Engineers, and CyanoHABs. Progress Report to Wasatch Front Water Quality Council. Salt Lake City, UT.

Scheffer, M., S. Carpenter, J. A. Foley, C. Folke, and B. Walker. Catastrophic shifts in ecosystems. Nature. Vol. 413. 591-596.

Scheffer, M., S. H. Hosper, M. L. Meijer, B. Moss & E. Jeppesen, 1993. Alternative equilibria in shallow lakes. Trends in Ecology and Evolution 8: 275–279.

Vilizzi, L., Tarkan, A.S., and G.H. Copp. 2015. Experimental evidence from causal criteria analysis for the effects of common carp Cyprinus carpio on freshwater ecosystems: a global perspective. Reviews in Fisheries Science and Aquaculture. 13(3): 253-290.

Walsworth, T.E., Landom, K. and Gaeta, J.W., 2020. Compensatory recruitment, dynamic habitat, and selective gear present challenges to large‐scale invasive species control. Ecosphere, 11(6): p.e03158

Walsworth, T.E., & Landom, K. 2021. Common carp population response to ongoing control efforts in Utah Lake. Annual report submitted to the June Sucker Recovery Implementation Program. Utah State University. 28 pp.

Walsworth, T.E., E. Wallace, and K. Landom. 2022. Common carp population response to ongoing control efforts in Utah Lake. DRAFT Annual report submitted to the June Sucker Recovery Implementation Program Project I.21.03 Carp population modeling. Department of Watershed Sciences, The Ecology Center, Utah State University Logan, UT 84322